The proposed work will continue along the main lines which have been pursued in this laboratory for the past more than 15 years. The project deals with developing and using procedures for quantitative autoradiography on the electron microscope (EM) level. In the current year, I propose to concentrate on four main aspects of this work: 1) To utilize computer graphics in analyzing EM autoradiograms. This would involve adapting our previously devised methods, based on the resolution of the autoradiographic preparation, and will facilitate our ability to test large numbers of hypotheses in order to determine the most likely distribution of radioactive sources in a tissue. 2) To devise a method for preparing EM autoradiograms for soluble compounds. This involves calibrating a dry mounting stripping film. 3) Obtain the resolution and detailed grain distributions for isotopes with energy higher than that of 14C. Currently, the effort is on 45Ca. 4) To utilize these new procedures, combined with a high resolution emulsion, to determine the detailed pathway of secretory materials through the Golgi apparatus of pituicytes.